Caulerpa taxifolia is a favourite green macro algae of marine aquarium hobbyists around the world. It can grow rapidly and under a wide variety of lighting conditions, providing a great method of exporting nutrients from an aquarium. However, these desirable properties and the fact it has few predators, have created some major problem for marine habitats where it has been introduced as a non-native species. C. taxifolia can spread as a carpet, out competing native aquatic algae and grasses, totally changing the ecosystem's balance as the organisms dependent on the native vegetation move or die out.
Description
C. taxifolia, showing the stolons (running left to right), attached fronds (pointing up) with pinnules, and the regular spaced rhizoid pillars (pointing down) with filamentous rhizoids for substrate attachment.
Being an alga, C. taxifolia does not have the same type structures as plants, but there are ones that fullfil similar purposes. The central part is the stolon, which acts like a stem, from which the fronds and rhizoids are attached. The stolon is how the algae grows and spreads, sending these out as a runner. The fronds, which are like the leaves, grow directly from the stolons at regular intervals, with the size is dictated by the light intensity (higher the light intensity, the shorter they become). The fronds are made up of pinnules that grow along either side of the frond. Also at regular intervals, rhizoid pillars decend from the stolons, with thin filamentous rhizoids, which are like the roots, attached. These rhizoids provide a means to attach to the substrate and may also be involved in some nutrient uptake. Additionally, being an alga means that a single individual “plant” is actually a single cell.
Close up of the C. taxifolia fronds.
Reproduction is by fragmentation, with only male gametes being released by the problematic Mediterranean strain when it goes sexual. However, the wild, native strains will release male and female gametes. The ease of regrowth from fragments is one of the reasons why it can be such a problem, all it takes is a small fragment to be transported to a new location and rapid growth from that can occur. The Mediterranean strain of C. taxifolia can also withstand severe nutrient limitation, low temperatures (7oC is lethal minimum temperature for the Mediterranean strain, 14oC for the normal, tropical strains) and can grow under low light conditions. The optimum growth temperature is in the region of 20-30oC ( 32oC is the lethal maximum temperature).
Around the World
C. taxifolia is native to the topical oceans and seas, including; the Atlantic Ocean (West Indies and the African Coast), Indian Ocean (Pakistan, Sri Lanka and north western Australia) and Pacific Ocean (Philippines, Indonesia, Japan, New Caledonia and north eastern Australia). In these areas it is not a problem, only forming smaller, locatised growths. However, introduction into regions where it is non-native has become a very significant problem.
Mediterranean Sea
The suitability of C. taxifolia for use in the marine aquarium was discovered by the tropical saltwater aquarium curator at the Wilhelmina Zoo (Stuttgart), and it then made its way around the world to many public aquariums. It is reported that during its captive breeding it was exposed to various chemicals and ultraviolet light, altering and switching on genes not previously present, expressed or active in the wild.
In 1982, a sample made it to the Oceanographic Museum of Monaco and two years later it was discovered in the waters outside the museum as a patch of only a square metre. By 1989 it has spread to 1 hectare and the following year it was detected 100km west of Monaco at Cap Martin and Toulon. Since then it has continually spread and formed large meadows totally carpetting the seafloor. By 2001, the infestation was estimated to be over 12,000 hectares, spanning from Spain to the Adriatic Sea and even on the southern shores of the Mediterranean. The missed opportunity of destruction of the released algae in the first couple of years means now that the infestation is essentially uncontrollable. Except for several attempts at controlling the spread in Italy when it was first spotted there, no control strategy has been fully established. Future biological controls may be found that can help to reduce the impact, but it is most likely now there to stay.
In March 1993, the French Minister for the Environment and the State Undersecretary for the Sea banned the offering, the sale, buying, use and dumping into the sea of all or parts of the specimens of the algae C taxifolia. It has also been included on the Mediterranean level by two provisions of article 13 of the Barcelona Convention's Protocol on Specially Protected Areas, adopted in 1996: “The introduction of non-indigenous or genetically modifies species”.
Southern California
In June 2000, C. taxifolia was found in Agua Hedionda Lagoon (San Diego County) and then in July 2000 in a section of Huntington Harbour (Orange County), on the southern Californian coast. Eradication efforts has been much swifter, with people wanting to avoid the problems that have occurred in the Mediterranean.
Legislation was subsequently past (Assembly Bill 1334) in September 2001 to prohibit the sale, possession and transportation of C. taxifolia in California. The City of Sand Diego also adopted an ordinance banning the possession, sale and transportation of the entire Caulerpa genus within city limits. Additionally, importation of the Mediterranean stain into United States, and interstate trade, is now a federal offense under the Federal Noxious Weed Act of 1999 and the Plant Protection Act of 2000.
Eradication is being attempted, with divers placing tarpaulins over the areas and bleach placed underneath to kill the algae. It appears to have been successful.
Florida
C. taxifolia is a native of the Florida Keys. To ensure that the Mediterranean strain does not manage to get a foot hold, a monitoring and dectection system has been put into place by the Florida Department of Agriculture and Consumer Service, Division of Aquaculture.
Australia
The Australian Quarantine and Inspection Service recognised the risk of and introduction of a non-native C. taxifolia and the importation was banned in 1996. However, in 2000 there were patches sighted in Port Hacking, Lake Conjola and Careel Bay in New South Wales, and this was followed by then Narrawallee Inlet, Burrill Lake, Pittwater and Lake Macquarie in New South Wales and West Lakes and Port River in South Australia in 2001.
Legal Status
Victoria
No sightings have been made of C. taxifolia within Victorian waters. However, due to the possibility of infestation as the water conditions are similar to that found in South Australia and New South Wales, it was declared a noxious species from November 2004. From this date a person must not be in possession of this algae.
According to the Victorian Department of Primary Industries - Fisheries and Aquaculture web site, an amnesty period has been established - "To allow people to dispose of this species, a 90 day amnesty period will apply from 11 November 2004 to 8 February 2005. During this period, people who possess this species should dispose of it in the recommended manner." Possession of C. taxifolia after this period can incur a fine of up to $10,000 for a first offence and $20,000 for a second offence.
New South Wales
Within the state of New South Wales, it was listed as a noxious marine vegetation in October 2000 and cannot be bought, sold or traded with fines of up to $11,000 for breaking these rules. It was allowable to keep it within a fully contained aquarium until December 2004, but it has now been upgraded to a prohibited species.
South Australia
For South Australia, it has been class as a marine pest and it is an offence to import, sell or possess C. taxifolia. Fines of up to $4,000 apply.
Western Australia
Western Australia currently has C. taxifolia listed as a high risk invasive species. It has not to date been recorded within the state, although it should be native to the northern sections of the state.
Tasmania
There has not been any sightings of C. taxifolia within Tasmanian waters and there is currently no quarantine barriers to importation of the algae into the state, but doing so would be highly irresponsible. It is likely that the Tasmania government will take some action on this in the future.
Queensland and Northern Territory
The legal status of this algae within the states of Queensland and the Northern Territory is not known at this time. It is unlikely to be considered due to the fact that it is native to these areas and should not cause any infestations.
Current Information
For up to date information on the legal status of C. taxifolia, here are the links to information for each Australian state:
A number of different techniques have been trialed in an attempt to halt the spread, including those listed below. Total eradication is next to impossible to achieve if an infestation is allowed to reach significant proportions, as has occurred in the Mediterranean Sea. However, for smaller infestations it may be possible, as has been observed in Southern California. Successful elimination with the Australian infestations is yet to be seen as the various control techniques are still being trialed to find one that will work under local conditions.
Manual uprooting by divers: highly ineffective except for very small patches, all it takes it for a single fragment to remain and regrowth will occur.
Mechanical removal by underwater suction devices: same as with manual removal.
Chemical control using copper (partially effective and can slow spread), chlorine (effective, but kills everything) and algacides (ineffective)
Extremes in salinity, both high and low: still being evaluated how successful this is in Australia.
Biological control using predatory Opisthobranch Mollucs, Oxynoe olivacea, O. azuropunctata, Lobiger serradifalci and Elysia subornata: the former Mediterranean native species are ineffective and success relies on finding a low temperature tolerant strain of the last (tropical) species listed.
Disposal
If you are a marine hobbyist within Victoria or South Australia then you need to destroy any C. taxifolia in your possession. For those in other states it would also be recommended to do the same thing, removing its presence entirely from the hobby and reducing the risk of release into the wild. The infestations may not have been due to an aquarist, but it is best if the risk is totally removed. There are also other suitable alternatives to this algae, so there is no need to have it within your marine aquarium.
The recommended disposal method is to place it within a plastic bag in the freezer for at least 24 hours hours. Then dispose of the frozen material in a rubbish bin, still within the plastic bag. Do not release it by flushing it down the toilet, sink or placing it in a drain or waterway.
The information provided here was correct at the time of publication to the best of the knowledge of the author. The author is not liable for any inaccuracies to the status of the laws of the applicable states or countries. Check with the appropriate government department for the most current and up to date information.
